Re: The cost in kW
It is a function of the number of people trying to mine coins, which in turn is related to the value of the coin. So, price goes up, electricity consumption goes up.
If you wanted to mount a 51% attack on the network, you would need the electricity supply of a medium-sized country at your disposal in order to carry it out. That's not possible, so that's what makes Bitcoin secure. The vast amounts of power used is a necessary feature of Bitcoin's proof of work algorithm, and unlike, previous IT inventions, it won't improve with improved hardware.